Identification by fingerprints includes a stage of acquiring an image of at least one fingerprint of a candidate for identification and a stage of processing the image to enable it to be compared with digitized fingerprint images, or with representations of such fingerprints that have been processed to show up the characteristics thereof (representations known as templates), stored in a database together with the identify of the proprietor of each of them.
Identification techniques using fingerprints are in widespread use in the context of police investigations, and they are tending to become more and more widely used for frontier controls or merely for checking identities, e.g. on entering premises to which access is regulated, such as airports, businesses, . . . .
This increase in the field of application of these techniques has resulted in particular in an improvement in the devices for acquiring fingerprint images and in the image processing systems that are associated therewith; there has also been a reduction in the cost of the computer means needed to implement them.
In these new applications, acquisition devices are used by people untrained in their use and without help from a qualified operator. In addition, in certain applications such as frontier controls a rejection can be very penalizing and can require verification by a specialized person, thereby increasing the duration of the control. The ergonomics of the acquisition device therefore need to be particularly well thought out in order to avoid wrong utilization. To improve the reliability of the verification, it has also been envisaged to perform identification on the basis of a plurality of fingerprints.
The improvement in processing methods combined with the increase in the calculation power of computer means have made it possible to reduce the time required for processing which is becoming negligible compared with the time required for acquisition, in particular when identification requires images to be acquired of a plurality of fingerprints (several different fingers).
Acquisition is generally performed by means of a device comprising a stand defining an acquisition zone that extends substantially in a plane, an acquisition member that is secured to the stand so as to have a sensing face forming the acquisition zone, and a processor unit connected to the acquisition member for processing a signal coming therefrom. The user presses a finger against the sensing face (or several fingers simultaneously or in succession, where appropriate). That mode of operation is particularly slow, and the finger must be stationary since otherwise the fingerprint cannot be acquired. Furthermore, in certain circumstances and for certain people, the skin of the fingers is particularly dry and does not enable acquisition to be performed of quality that is sufficient to guarantee good performance without waiting several tens of seconds. Finally, contact between the fingers and the sensor dirty the sensor, thereby degrading the quality of the images and thus requiring periodic cleaning, and above all being perceived by users as being unhygienic.
Systems with contact do not enable acceptable images to be acquired of palms under conditions that are ergonomic. In order to obtain an image of an entire palm, it is necessary for it to come fully into contact with the acquisition surface, and that is not generally possible and requires the hand to be flattened hard against the device.